Our invention relates to function control apparatus, and particularly to function control apparatus for synchronizing a receiver that receives binary messages so that the beginning of each binary message can be accurately determined.
Radio communication systems, particulary those having a command or base station and one or more controlled stations, such as a mobile station, provide various functions over and above the simple call and answer voice communication. These functions include, among others, a base station determining the status or condition of a particular mobile station in a system, or establishing voice communications between two or more stations in the system. In systems where such functions are provided by binary messages, a receiver must synchronize with the binary message in order to determine the exact binary pulse which starts the message. Otherwise, the message will be meaningless or lost.
Accordingly, a primary object of our invention is to provide new and improved function control apparatus having an arrangement for synchronizing a radio receiver with received binary messages to insure that an accurate binary message is received.
Another object of our invention is to provide new and improved function control apparatus which enable a receiver to accurately determine when it is in synchronization with a transmitted binary message and to give signals indicating when such synchronization is present and absent.
Once synchronization with received binary messages is achieved, it is desirable to maintain such synchronization unless synchronization is lost for a relatively long period of time, certainly longer than would normally occur from radio fading, or noise, or interference.
Accordingly, another object of our invention is to provide new and improved function control apparatus which enable receiving equipment to synchronize itself with transmitted binary messages, and to maintain such synchronization despite occasional losses of the binary messages and until a predetermined number of such losses occur in continuous sequence.
Another object of our invention is to provide new and improved function control apparatus which produces an in-synchronization signal after a first plurality of predetermined synchronizing binary words are properly received, and which produces an out-of-synchronization signal after a second plurality of the predetermined synchronizing binary words are improperly received consecutively and without any intermediate properly received synchronizing words.